The use of a viscous sealant layer generally arranged in the inner cavity of the tyre has been known for some time. In particular, the sealant layer is generally arranged in contact with the inner liner layer in the area of the tread strip. The object of the sealant layer is to surround and adhere to the object that has penetrated the tread, thus preventing air from leaking out of the tyre by means of instantaneous “sealing”. Furthermore, if the penetrated object exits from the tread, the material of the sealant layer will occupy the hole left by the object, sealing it.
The viscosity of the sealant layer is one of the most important parameters for the effectiveness of said sealant layer. In fact, the viscosity of the sealant layer must be able to guarantee both the sealing action on the penetrated object and on the hole left by the object as described above, and its stability in the inner cavity of the tyre regardless of the static or dynamic conditions of the tyre. As is known to a person skilled in the art, a correct viscosity of the sealant layer necessarily results in a high surface stickiness of said layer. While a certain stickiness of the surface of the sealant layer which in use is in contact with the inner liner layer can be useful, for the opposite surface, i.e. the one exposed to the air, it can constitute a serious problem. In fact, during storage of the tyre, foreign materials such as dust, leaves or even insects stick on the surface of the sealant layer exposed to the air. This necessarily downgrades the commercial value of the tyre with obvious financial consequences for the manufacturers and the dealers.
The need was therefore felt for a sealant layer having the required viscosity characteristics in order to correctly perform its function but which, at the same time, has a low stickiness on the surface exposed to the air such as to avoid the drawbacks described above.
The inventors of the present invention have surprisingly found that the application of a UV radiation on the surface exposed to the air of the sealant layer drastically reduces its stickiness, without modifying the characteristics of the sealant layer overall and, therefore, without compromising its effectiveness.